1. Field of the Invention
The present invention relates to a signal processing device and method, and a signal processing program used therein and more particularly to a signal processing device and method, and a signal processing program used therein realizing more ready and sure noise removal.
2. Description of the Related Art
As a method of removing noise from an input signal by performing filter processing, a method in which a plurality of filter processing units are series-coupled to perform a plurality of filter processing operations in series (hereinafter, referred to as a method of series-coupling a plurality of filter processing operations) is well known. Series-coupling a plurality of filter processing operations may cause an increase in capacity of memory necessary for holding input signals in terms of hardware and may cause an increase in processing time which is difficult to divide in terms of software. In addition, in the case that a plurality of filter processing operations are series-coupled, it may sometimes occur that an appropriate filter processing operation is not performed on an input signal at a succeeding stage, due to the influence of a change in the input signal induced by a filter processing operation performed at a previous stage.
Thus, methods in which a plurality of filter processing units are parallel-coupled to perform a plurality of filter processing operations in parallel (hereinafter, referred to as a method of parallel-coupling a plurality of filter processing operations) have been proposed. As examples of such methods, mainly, the following three methods are well known.
As the first method, there is a method of realizing parallel-coupling of a plurality of filter processing operations by calculating a running average using input signals on which a plurality of filter processing operations have been performed respectively using a plurality of filters. As the second method, there is a method of obtaining a difference between an input signal and an input signal on which a filter processing operation has been performed for each filter to add the difference obtained for each filter processing operation to the input signal.
As the third method, there is a method of switching a filter used for a filter processing operation for each region of an input image formed on the basis of an input signal. As an example of the third method, there has been proposed a method in which an input image is divided into pixel blocks and a filter for block noise reduction is switched to a filter for mosquito noise reduction or vice versa for each pixel block to perform a filter processing operation using either one of these filters to reduce artifacts appearing on the input image, for example, as disclosed in Japanese Laid-Open Patent Publication No. 2005-318614.